The Long Term Evolution (LTE)/Long Term Evolution-Advanced (LTE-A) system is a scheduling-based communication system, that is, if there is data to be transmitted in the transmission buffer of a User Equipment (UE), the UE firstly transmits a Buffer Status Report (BSR) to a base station to notify the base station of information of the data to be transmitted in the transmission buffer of the UE. Upon reception of the BSR transmitted from the UE, the base station will allocate the related Uplink-Shared Channel (UL-SCH) resource to the UE according to the amount of the data to be transmitted of the UE and the service type and instruct the UE to transmit the data on the allocated UL-SCH resource.
The UE transmits the BSR to the base station also on the Uplink-Shared Channel (UL-SCH) resource, and if there is a BSR to be transmitted but no uplink-shared channel resource is available, a Scheduling Request will be triggered to request the base station to allocate an uplink-shared channel resource for the BSR to be transmitted.
After the SR is triggered, the SR may be transmitted in either of two ways, i.e., the SR is transmitted on a Dedicated Scheduling Request (D-SR) resource or in a Random Access procedure (RA-SR). When the UE and the base station are synchronized, there may be no available D-SR resource, and when they are unsynchronized, there must be no D-SR resource. D-SR resource is allocated by RRC signaling and transmits on Physical Uplink Control Channel (PUCCH).
Generally, an SR is transmitted under such a fundamental principle that no RA-SR will be used so long as the D-SR resource is available. And the SR can be transmitted repeatedly on the D-SR resource until the UE gets the uplink-shared channel resource allocated by the base station.
In the LTE system, an uplink dedicated scheduling request is transmitted on PUCCH according to PUCCH format1/1a/1b for which a symbol is spread in the frequency domain by being multiplied with a 12-bit cyclic shift sequence to form a 12-bit sequence of symbols, which is in turn spread in the time domain by being multiplied with a 4-bit orthogonal sequence and mapped onto 12×4 time and frequency locations of a Physical Resource Block (PRB) on a timeslot, where three symbols are used for transmission of a Reference Signal (RS), and different users borne on the same PRB are distinguished with different cyclic shift values for a fundamental sequence.
In the system, a part of the PUCCH resource is typically reserved for each subframe as a cell-specific SR resource so that the PUCCH resource is shared amongst UEs in the cell and the base station allocates the cell-specific SR resource to the UEs in the cell according to a specific resource allocation strategy and notifies the D-SR PUCCH resource index, period and subframe offset to the UE by RRC signaling. The meanings of parameters in the RRC signaling are depicted in Table 1, where the RRC signaling includes sr-PUCCH-ResourceIndex, sr-ConfigurationIndex and dsr-TransMax, with their meanings as depicted in the table.
TABLE 1ParameterThe Meaning of Parametersr-PUCCH-This parameter designates a resource index of aResourceIndexPUCCH resource in a subframe, which is allocatedto the UE for transmission of a D-SR.sr-This parameter represents the period and subframeConfigurationIndexoffset by which a D-SR is transmitted, UE candetermine its D-SR resource according to thisparameter and the starting subframe of the D-SRresource.dsr-TransMaxThis parameter represents the maximum number oftransmissions that a D-SR can be transmitted,and the purpose of introducing this parameteris to improve the reliability of the D-SR.
The peak rates of the LTE-A are significantly increased compared with the LTE system, and 1 Gbps in the downlink and 500 Mbps in the uplink are required. Also the LTE-A system is required to be well compatible with the LTE system. Carrier Aggregation (CA) has been introduced to the LTE-A system in order to reach the increased peak rates, compatible with the LTE system and full use of the spectrum resource.
Carrier aggregation means that UE can aggregate more than one cell simultaneously, which is different from the legacy radio systems who can only aggregate one cell at a time. In a system supporting carrier aggregation, component carriers may or may not be continuous, and for compatibility with the LTE system, the maximum bandwidth of each component carriers is 20 MHz, and the bandwidths of different component carriers may be same or not.
As for the definition of a primary carrier, a plurality of component carriers may be supported in the uplink in the LTE-A system, and there is no definite concept of a primary carrier so far, which may be cell-specific or UE-specific. If the primary carrier is cell-specific, the primary carrier has to be supported by all of the R10 UEs; and if the primary carrier is UE-specific, the UE has to support its own primary carrier.
With the introduction of CA, a plurality of component carriers have to be supported concurrently in the uplink, so how to configure a UE-specific D-SR resource shall be taken into account in the case of a plurality of component carriers, but a relevant description is absent in the existing standards.